An object of mass m is tied to a string of length L and a variable horizontal force is applied on it which starts at zero and gradually increases until the string makes an angle Theta with the vertical. The work done by the force F is

1. mgL(1-sin(th))
2. mgL
3. mgL(1-cos(th))
4. mgL(1+cos(th))

I got the answer as mgL(1-cos(th)).. but the answer is given mgL(1+cos(th)). I am confused, please explain the answer

Three identical balls are placed on a frictionless horizontal surface touching each other. They stick to each other because of adhesive. Another ball of same radius and mass m is placed over the void created by the three balls. Find the forces applied by the balls kept on the floor to each other if the system remains in equilibrium.

A car loaded with water having total mass 1000 kg moves on a straight horizontal Road starting from rest under the action of a force of 100 Newton. The water spills throw a small hole in the bottom at a rate of 0.1 KG per second the velocity of cart after 300 seconds is nearly.

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